The ecology and behaviour of eucalypt-feeding caterpillars in response to predation risk

Abstract

It was traditionally assumed that predator effects were lethally transmitted, however there is now increasing evidence of the importance of their non-consumptive effects. I outline a conceptual framework that integrates both the consumptive and non-consumptive pathways for predator effects on insect herbivores. Using this framework, I aimed to improve our understanding of predator effects on insect herbivores in the Eucalyptus system. First I investigated how the plant traits- leaf age and location- affect predation risk, and also whether this risk varied with type of predator. I found no evidence for a difference in risk. I then manipulated head capsule stacks on Uraba lugens larvae to investigate their putative defensive function. I found that the retention of moulted head capsules provides some protection against natural enemies by serving as a false target as well as a weapon to fend off attackers. Next I investigated the behavioural responses of caterpillars to variation in a direct physical cue of predation risk, non-lethal predator attacks varying in location and frequency. I found that the type and extent of response varied according to the location and frequency of attack, suggesting that these caterpillars have the capacity to distinguish different levels of risk. I also investigated how both the behaviour and physiology of caterpillars are influenced by multiple cues of predation risk. I found that the direct physical cue invoked both short term behavioural responses and long-term physiological ones, while the indirect chemical cue invoked only short-term physiological responses. Finally my thesis also addressed a number of methodological aims regarding the use of model prey. I confirmed the validity of models as surrogates for real prey in a field setting. I also collated a comprehensive reference collection of attack marks and established guidelines for identifying predators responsible for attacks on models.